Rod length for the 5.3 and the LS1 (5.7) are the same which is 6.098". Rod length changes on many forged and stroker kits.

"Is it safe" I'm assuming means is it safe to bore to 3.898. Yes, it is.

You are essentially building an LS1 so use the recommended head gasket for an LS1.

Here where it's going to get tricky. The stock LS1 bore of 3.898 is very difficult to find forged pistons for. Mahle is the only one I know who makes one for your application. The part number from Texas Speed is 168-340898F04. They are pricey at $652 a set. Sucks doesn't it. Seems like all the manufacturers would have them but they all assume you'll be rebuilding a LS1 and would be boring your motor. So you can take it to the maximum bore of 3.905" and your piston selection gets greater but then you essentially are done as far as rebuilding in the future.

Rod length for the 5.3 and the LS1 (5.7) are the same which is 6.098". Rod length changes on many forged and stroker kits.

"Is it safe" I'm assuming means is it safe to bore to 3.898. Yes, it is.

You are essentially building an LS1 so use the recommended head gasket for an LS1.

Here where it's going to get tricky. The stock LS1 bore of 3.898 is very difficult to find forged pistons for. Mahle is the only one I know who makes one for your application. The part number from Texas Speed is 168-340898F04. They are pricey at $652 a set. Sucks doesn't it. Seems like all the manufacturers would have them but they all assume you'll be rebuilding a LS1 and would be boring your motor. So you can take it to the maximum bore of 3.905" and your piston selection gets greater but then you essentially are done as far as rebuilding in the future.

Just got off the phone with Wiseco and these are the pistons the had.

Wiseco - k392x3905 $752.52 -25cc dish
k444x3903 $752.52 -11cc dish

You were saying that I can go to a 3.903 bore, how about to a 3.905? I am not looking to reuse this block in the future.